The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed.
For example, lithography is a technique frequently used in IC manufacturing for transferring an IC design to a semiconductor substrate. A typical lithography includes: coating a resist (or photoresist) layer over a substrate; using a mask, exposing the resist layer; developing the resist layer to leave a patterned resist layer over the substrate; and etching the substrate to form a patterned image. One quality measure of the lithography process is the etched images' critical dimension (CD) uniformity, which directly impacts the IC production yield. As the semiconductor process continues to scale down, it is generally desirable to improve the CD uniformity of after-etch images.